82 
MESSES. G. F. C. SEAELE AE^D T. G. BEDFOED 
measuring hysteresis, for the observations for the tirst four values of the magnetic 
force, involving fifty-two determinations of hysteresis, were easily taken in one day, 
though much time was spent in changing tlie load, in putting the current through 
20 reversals before the magnetic tests were made, and in bringing the suspended coil 
of the dynamometer to rest. 
t/ 
Ejfect of Torsion beyond the Elastic Limit. 
§ 59. So far our exiDeriments were made for torsional strains in which the elastic 
limit was not overpassed at all, or in any case was not exceeded to such an extent 
that the wire took a noticeable permanent set. AVe thought it would he interesting 
to trace the effect of great torsional overstrain upon the induction and the hysteresis 
for a constant maximum magnetic force Hq = 5. In 1899 we made experiments in 
this direction upon two specimens of the same soft iron wire as was used in the 
experiments of §§ 57, 58. Both specimens were heated in a large blo^vpipe flame 
to burn off the zinc coating and to anneal the wire. The arrangement of § 53 was 
used for applying torsion. 
§60. Experiments on Soft Iron Wire (1); Hq = 5.—In these exjDeriments the 
Avheel was turned, always in one direction, through the desired angle, ineasured from 
its position when the wire was unstrained, and was then clamped. A mechanical 
“counter” served to record the number of revolutions made by the Avheel. AVhen 
the wheel had been clamped in any position, the magnetic force was put through 
20 cycles of reversal, and then readings for Bq and W were made. The wheel 
was now turned still further and again clamped, and then the magnetic observations 
were repeated. This process was continued till the wire broke. The fracture 
occurred when the wheel had been tuiaied throua:!! 104 revolutions. Since the leno-th 
of the wire was 65‘5 centims., this angle corresponds to a twist of 1'57 turns per 
centim. The observations were too numerous to be recorded in a table ; we therefore 
only give a diagram in hg. 12, distinguishing the curves for this specimen by the 
mark (l). 
In these experiments the first residt of the torsion was to cause a very rapid 
diminution of both Bq and AV. The curve for B,, falls continuously till the wire 
breaks, but the curve for AV shows a well-marked rise and fall, with a maximum at 
about 7‘5 revolutions. The values of Bq and AV were determined immediately after 
the wire broke, the tests showing that, when the stress was relieved by the fracture, 
both Bq and AV fell to about half the values they had just before the fracture. Thus 
Bq fell from 2950 to 1510, while AV fell from 2410 to 1044. 
AVe found that when the wire had been twisted AA^ diminished considerably with 
continued reversals, even after 20 cycles of magnetisation. 
§ 61. Experiments on Soft Iron Wire (2); Hq = 5'0.—The second specimen (2) was 
treated rather differently. The wheel was turned through a definite number of 
